Optical terminator, optical wavelength filter, and external resonator-type laser light source

Abstract

An optical termination device (30) is provided with a first termination waveguide (50). The first termination waveguide (50) includes a curved waveguide (51) and a curved waveguide (52). The curved waveguide (51) includes a unique maximum curvature portion (51m). The curved waveguide (52) includes a unique maximum curvature portion (52m). A first normal vector of the curved waveguide (51) in the maximum curvature portion (51m) and a second normal vector of the curved waveguide (52) in the maximum curvature portion (52m) face the same direction as each other.

Description

Technical Field

[0001] The present disclosure relates to an optical terminator, an optical wavelength filter, and an external resonator type laser light source. Background Art

[0002] Japanese Patent Application Laid-Open No. 2021-39277 (Patent Document 1) discloses an optical terminator including a tapered portion and a curved structure portion.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2021-39277 Summary of the invention

[0006] However, in the optical terminal disclosed in Patent Document 1, the length of the curved structure is short, so the reflection of light cannot be fully suppressed in the optical terminal. In addition, the curved structure of the optical terminal disclosed in Patent Document 1 has a constant curvature throughout the curved structure, so the radiated light radiated from the curved structure cannot be made directional.

[0007] The present disclosure is made in view of the above-mentioned problems. The first mode of the present disclosure aims to provide an optical terminator that can further suppress the reflection of light and improve the directivity of the radiated light radiated from the optical terminator. The second mode of the present disclosure aims to provide an optical wavelength filter that can more accurately adjust the wavelength of light selected by the optical wavelength filter. The third mode of the present disclosure aims to provide an external resonator type laser light source that can accurately align the optical amplifier with respect to the optical wavelength filter and set the selected wavelength of the optical wavelength filter.

[0008] The optical terminator disclosed in the present invention comprises a substrate including a main surface and a first terminal waveguide formed on the main surface of the substrate. The first terminal waveguide comprises a first end, a first curved waveguide, a second curved waveguide, and a second end on the side opposite to the first end. The second curved waveguide is connected to the first curved waveguide and is arranged closer to the second end than the first curved waveguide. The first curved waveguide comprises a unique first maximum curvature portion. The first maximum curvature portion is a portion having the maximum curvature in the first curved waveguide. The second curved waveguide comprises a unique second maximum curvature portion. The second maximum curvature portion is a portion having the maximum curvature in the second curved waveguide. When viewed from above the main surface of the substrate, a first normal vector of the first curved waveguide in the first maximum curvature portion and a second normal vector of the second curved waveguide in the second maximum curvature portion are oriented in the same direction.

[0009] The optical wavelength filter disclosed in the present invention comprises the optical terminator disclosed in the present invention, a ring resonator, and a refractive index adjuster. The ring resonator is connected to the first end. The refractive index adjuster adjusts the refractive index of the ring resonator.

[0010] The external resonator laser light source disclosed in the present invention includes the optical wavelength filter disclosed in the present invention and an optical amplifier optically coupled to a ring resonator.

[0011] In the optical terminal disclosed in the present invention, light incident on the optical terminal is radiated from the first curved waveguide and the second curved waveguide. The intensity of the light reaching the second end of the optical terminal is reduced. The optical terminal can further suppress the reflection of light. In addition, the first normal vector and the second normal vector are oriented in the same direction, so the directivity of the radiated light radiated from the optical terminal can be improved.

[0012] The radiated light from the optical terminator of the present disclosure has higher intensity and higher directivity. Therefore, in the optical wavelength filter of the present disclosure, the wavelength of the light selected by the optical wavelength filter can be adjusted more accurately based on the radiated light from the optical terminator.

[0013] The radiated light from the optical terminator of the present invention has higher intensity and higher directivity. Therefore, in the external resonator laser light source of the present invention, the alignment of the optical amplifier with respect to the optical wavelength filter and the setting of the selected wavelength of the optical wavelength filter can be more accurately performed based on the radiated light from the optical terminator. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic plan view of the optical wavelength filter according to Embodiments 1 to 4.

[0015] Figure 2 The optical wavelength filter of embodiment 1 is Figure 1 A schematic cross-sectional view along section line II-II is shown.

[0016] Figure 3 This is a schematic plan view of a ring resonator included in the optical wavelength filter according to the first embodiment.

[0017] Figure 4 FIG. 1 is a diagram showing an example of a graph indicating a spectrum of light output from a through port of a ring resonator.

[0018] Figure 5 : is a diagram showing an example of a graph indicating the spectrum of light output from a drop port of a ring resonator.

[0019] Figure 6 This is a schematic partial enlarged plan view of the optical terminator according to Embodiment 1.

[0020] Figure 7 This is a diagram showing a graph indicating changes in the curvature of the optical terminator according to Embodiment 1.

[0021] Figure 8 This is a schematic partial enlarged plan view of the optical terminator according to the second embodiment.

[0022] Fig. 9 This is a diagram showing a graph indicating changes in the curvature of the optical terminator according to the second embodiment.

[0023] Fig.10 This is a schematic partial enlarged plan view of an optical terminator according to a modified example of the second embodiment.

[0024] Fig.11 This is a diagram showing a graph showing changes in the curvature of an optical terminator according to a modified example of the second embodiment.

[0025] Fig.12 This is a schematic partial enlarged plan view of an optical terminator according to Embodiment 3.

[0026] Fig.13 This is a schematic partial enlarged top view of an optical terminator according to a fourth embodiment.

[0027] Fig.14 This is a schematic partial enlarged plan view of an optical terminator according to a modified example of the fourth embodiment.

[0028] Fig.15 This is a schematic top view of an external cavity type laser light source according to a fifth embodiment.

[0029] Fig.16 The optical amplifier of the external resonator type laser light source included in the fifth embodiment Fig.15 A schematic cross-sectional view along section line XVI-XVI is shown. DETAILED DESCRIPTION

[0030] Hereinafter, the embodiment of the present disclosure will be described. In addition, the same reference numerals are attached to the same configurations, and the description thereof will not be repeated.

[0031] Implementation method 1.

[0032] Reference Figures 1 to 6, the optical wavelength filter 1 of the first embodiment is described. The optical wavelength filter 1 mainly includes ring resonators 20, 25, optical terminators 30, 31, 32, 33, a spectrum analyzer 48, and a controller 49. The optical wavelength filter 1 may further include a reflector 35, a waveguide 16, and an optical fiber 47. The ring resonator 20 includes waveguides 11, 13, a ring waveguide 12, a refractive index adjuster 21, and electrode pads 22, 23. The ring resonator 25 includes waveguides 13, 15, a ring waveguide 14, a refractive index adjuster 26, and electrode pads 27, 28. The optical terminators 30, 31, 32, 33 each include a first terminal waveguide 50 (see Figure 6 ).

[0033] The waveguides 11, 13, 15, 16, the ring waveguides 12, 14, and the first terminal waveguide 50 are formed on the main surface 10a of the substrate 10 (see Figure 2 ). The substrate 10 is, for example, a silicon substrate. The substrate 10 may be a compound semiconductor substrate such as an InP substrate or a glass substrate. The substrate 10 includes a main surface 10a. The main surface 10a extends in the x direction and the y direction perpendicular to the x direction. The normal direction of the main surface 10a is the z direction perpendicular to the x direction and the y direction. In this specification, forming a waveguide on the main surface 10a of the substrate 10 means forming a waveguide through the lower cladding layer 17 (see Figure 2 ) A waveguide is formed on the main surface 10a of the substrate 10 or a waveguide is directly formed on the main surface 10a of the substrate 10. The waveguides 11, 13, 15, 16, the ring waveguides 12, 14 and the first terminal waveguide 50 may also be formed through the upper cladding 18 (see Figure 2 )cover.

[0034] The waveguides 11, 13, 15, 16, the ring waveguides 12, 14, and the first terminal waveguide 50 have a higher refractive index than the lower cladding 17 and the upper cladding 18. Therefore, light propagates in the waveguides 11, 13, 15, 16, the ring waveguides 12, 14, and the first terminal waveguide 50. The lower cladding 17 and the upper cladding 18 are formed of, for example, SiO2. The waveguides 11, 13, 15, 16, the ring waveguides 12, 14, and the first terminal waveguide 50 are formed of, for example, silicon. The waveguides 11, 13, 15, 16, the ring waveguides 12, 14, and the first terminal waveguide 50 may be formed of either quartz or a semiconductor material.

[0035] like Figure 1 As shown, the waveguide 11 extends in the x direction, for example. The waveguide 11 includes an end 11a and an end 11b on the opposite side of the end 11a. The end 11a is the incident end of the optical wavelength filter 1 and the input port of the ring resonator 20. The end 11b of the waveguide 11 is the through port of the ring resonator 20 and is connected to the optical terminator 30.

[0036] The waveguide 13 extends, for example, along the waveguide 11. The waveguide 13 extends, for example, in the x direction. The waveguide 13 includes an end 13a and an end 13b on the side opposite to the end 13a. The waveguide 13 is optically coupled with the ring waveguide 12 and the ring waveguide 14. The ring waveguide 12 is arranged closer to the end 13b than the ring waveguide 14. The ring waveguide 14 is arranged closer to the end 13a than the ring waveguide 12. The waveguide 13 includes a drop port of the ring resonator 20, an input port of the ring resonator 25, and a through port of the ring resonator 25. The drop port of the ring resonator 20 is connected to the input port of the ring resonator 25. The end 13a of the waveguide 13 is a through port of the ring resonator 25 and is connected to the optical terminator 32. The end 13b of the waveguide 13 is connected to the optical terminator 31.

[0037] The waveguide 15 extends, for example, along the waveguide 13. The waveguide 15 extends, for example, in the x direction. The waveguide 15 includes an end 15a and an end 15b on the side opposite to the end 15a. The end 15b of the waveguide 15 is connected to the optical terminator 33. The waveguide 15 is optically coupled to the ring waveguide 14. The waveguide 15 includes a drop port of the ring resonator 25. The end 15a of the waveguide 15 is the drop port of the ring resonator 25 and is connected to the reflector 35.

[0038] The reflector 35 reflects all or part of the light incident from the end 15a of the waveguide 15 to the waveguide 16. The reflector 35 is, for example, a dielectric multilayer film reflector inserted into a groove formed in the cladding (upper cladding 18 and lower cladding 17). The waveguide 16 includes an end 16a and an end 16b on the opposite side of the end 16a. The end 16b of the waveguide 16 is opposite to the reflector 35. All or part of the light reflected by the reflector 35 is incident on the end 16b of the waveguide 16, and is emitted from the end 16a of the waveguide 16 as light 46. The end 16a of the waveguide 16 is the emission end of the optical wavelength filter 1.

[0039] Reference Figure 1 as well as Figures 3 to 5 , illustrating the wavelength selection function of the ring resonator 20.

[0040] Light 40 is incident from the input port (end 11a) of the ring resonator 20. Light 40 advances in the waveguide 11 without coupling with the ring waveguide 12 according to the wavelength of light 40, and becomes light 41 emitted from the through port (end 11b) of the ring resonator 20 (see Figure 3 as well as Figure 4 ) or coupled with the waveguide 13 via the ring waveguide 12, and becomes the light 42 emitted from the drop port of the ring resonator 20 (refer to Figure 3 as well as Figure 5 ).like Figure 5As shown, the wavelength of the light 42 emitted from the drop port of the ring resonator 20 is determined by the refractive index n of the ring waveguide 12 and the length L of the ring waveguide 12. The free frequency range (FSR) of the ring resonator 20 is provided by equation (1). The FSR of the ring resonator 20 is the interval of frequencies at which the optical coupling rate from the input port of the ring resonator 20 to the drop port of the ring resonator 20 becomes maximum. Therefore, the wavelength of the light 42 output from the drop port of the ring resonator 20 can be selected. The ring resonator 20 functions as an optical wavelength filter.

[0041] FSR=c / (nL) (1)

[0042] Here, c represents the speed of light in a vacuum.

[0043] The refractive index adjuster 21 adjusts the refractive index of the ring waveguide 12. Therefore, the ring resonator 20 functions as a wavelength variable filter. Specifically, the refractive index of the ring waveguide 12 is changed by the refractive index adjuster 21. The free frequency range (FSR) of the ring resonator 20 changes, and the wavelength of the light 42 coupled to the drop port of the ring resonator 20 changes.

[0044] In this embodiment, the ring waveguide 12 is formed of a material having a thermo-optic effect such as silicon, and the refractive index adjusters 21 and 26 are thin film heaters capable of applying heat to the ring waveguide 12. The thin film heater is formed of a high-resistance metal material such as tantalum, platinum or titanium. The refractive index adjuster 21 is connected to the electrode pads 22 and 23. Power is supplied to the refractive index adjuster 21 via the electrode pads 22 and 23.

[0045] The through port (end 11a) of the ring resonator 20 is connected to the optical terminator 30. Based on the radiated light 44 radiated from the optical terminator 30, the power supplied to the refractive index adjuster 21 is adjusted.

[0046] Specifically, the spectrum analyzer 48 receives the radiated light 44 from the optical terminator 30 via the optical fiber 47. The spectrum analyzer 48 obtains the spectrum of the radiated light 44. The controller 49 is connected to the spectrum analyzer 48. The controller 49 receives the spectrum of the radiated light 44 from the spectrum analyzer 48. The controller 49 controls the power supplied to the refractive index adjuster 21 according to the spectrum of the radiated light 44. The temperature of the refractive index adjuster 21 is appropriately adjusted to appropriately adjust the refractive index of the ring waveguide 12. For example, the power supplied to the refractive index adjuster 21 is adjusted so that the spectral intensity of the wavelength to be selected by the optical wavelength filter 1 in the radiated light 44 from the optical terminator 30 becomes minimum. In this way, the optical coupling rate of the light having the wavelength to be selected by the optical wavelength filter 1 to the drop port of the ring resonator 20 can be maximized.

[0047] In the ring resonator 25, it operates as a wavelength variable filter similarly to the ring resonator 20. The power supplied to the refractive index adjuster 26 is also controlled by the controller 49 similarly to the refractive index adjuster 21. For example, the power supplied to the refractive index adjuster 26 is adjusted according to the radiated light radiated from the optical terminator 32. However, the length of the ring waveguide 14 is different from the length of the ring waveguide 12. Therefore, the FSR of the ring resonator 25 is different from the FSR of the ring resonator 20.

[0048] The optical terminators 31, 32, and 33 are configured similarly to the optical terminator 30 and function similarly. Figure 6 as well as Figure 7 , the optical terminator 30 is described in detail.

[0049] The optical terminator 30 includes a substrate 10 (see Figure 1 as well as Figure 2 ) and a first terminal waveguide 50 formed on the main surface 10a of the substrate 10. The optical terminator 30 may also include a lower cladding layer 17 (see Figure 2 ) and the upper cladding 18 (refer to Figure 2 ). The first terminal waveguide 50 is a spiral waveguide 50a when viewed from above the main surface 10a of the substrate 10. The first terminal waveguide 50 includes a first end 57, curved waveguides 51, 52, 53, 54, 55, and a second end 58 on the opposite side to the first end 57.

[0050] The first end 57 of the first terminal waveguide 50 is connected to the end 11b of the waveguide 11 as the through port of the ring resonator 20. The first end 57 is the optical input end of the optical terminator 30. The second end 58 is the end of the optical terminator 30. The second end 58 is located at the center of the spiral of the first terminal waveguide 50.

[0051] The curved waveguide 51 includes a first end 57 connected to the end 11b of the waveguide 11. The curved waveguide 51 has a spiral shape of one turn when viewed from the main surface 10a of the substrate 10. The curved waveguide 51 includes a single maximum curvature portion 51m. The maximum curvature portion 51m is a portion having the largest curvature in the curved waveguide 51. The curved waveguide 51 includes a curved waveguide portion 51a and a curved waveguide portion 51b.

[0052] The curved waveguide portion 51a is connected to the waveguide 11 and includes a first end 57 of the first terminal waveguide 50. The curved waveguide portion 51a extends toward the outside of the substrate 10 (for example, in the +x direction (see FIG. 1 ) when the principal surface 10a of the substrate 10 is viewed from above. Figure 1The curved waveguide portion 51a includes a maximum curvature portion 51m. The curved waveguide portion 51b is connected to the curved waveguide portion 51a. The curved waveguide portion 51b is arranged closer to the second end 58 than the curved waveguide portion 51a. The curved waveguide portion 51b extends toward the inner side of the substrate 10 (e.g., in the −x direction (refer to FIG. 1 )) when the main surface 10a of the substrate 10 is viewed from above. Figure 1 ))Expansion.

[0053] The curved waveguide 52 is connected to the curved waveguide 51. When viewed from above the main surface 10a of the substrate 10, the curved waveguide 52 has a spiral shape of one turn. The curved waveguide 52 is arranged on the inner side of the curved waveguide 51. The curved waveguide 52 is arranged closer to the second end 58 than the curved waveguide 51. The curved waveguide 52 includes a single maximum curvature portion 52m. The maximum curvature portion 52m is a portion having the largest curvature in the curved waveguide 52. The curved waveguide 52 includes a curved waveguide portion 52a and a curved waveguide portion 52b.

[0054] The curved waveguide portion 52a is connected to the curved waveguide portion 51b. The curved waveguide portion 52a extends toward the outside of the substrate 10 (for example, in the +x direction (see FIG. 1 ) when the principal surface 10a of the substrate 10 is viewed from above. Figure 1 The curved waveguide portion 52a includes a maximum curvature portion 52m. The curved waveguide portion 52b is connected to the curved waveguide portion 52a. The curved waveguide portion 52b is arranged closer to the second end 58 than the curved waveguide portion 52a. The curved waveguide portion 52b extends toward the inner side of the substrate 10 (e.g., in the −x direction (refer to FIG. 1 )) when the main surface 10a of the substrate 10 is viewed from above. Figure 1 ))Expansion.

[0055] The curved waveguide 53 is connected to the curved waveguide 52. The curved waveguide 53 has a spiral shape of one turn when viewed from above the main surface 10a of the substrate 10. The curved waveguide 53 is arranged on the inner side of the curved waveguide 52. The curved waveguide 53 is arranged closer to the second end 58 than the curved waveguide 52. The curved waveguide 53 includes a single maximum curvature portion 53m. The maximum curvature portion 53m is a portion having the largest curvature in the curved waveguide 53. The curved waveguide 53 includes a curved waveguide portion 53a and a curved waveguide portion 53b.

[0056] The curved waveguide portion 53a is connected to the curved waveguide portion 52b. The curved waveguide portion 53a extends toward the outside of the substrate 10 (for example, in the +x direction (see FIG. 1 ) when the principal surface 10a of the substrate 10 is viewed from above. Figure 1 The curved waveguide portion 53a includes a maximum curvature portion 53m. The curved waveguide portion 53b is connected to the curved waveguide portion 53a. The curved waveguide portion 53b is arranged closer to the second end 58 than the curved waveguide portion 53a. The curved waveguide portion 53b extends toward the inner side of the substrate 10 (e.g., in the −x direction (refer to FIG. 1 )) when the main surface 10a of the substrate 10 is viewed from above. Figure 1 ))Expansion.

[0057] The curved waveguide 54 is connected to the curved waveguide 53. When viewed from above the main surface 10a of the substrate 10, the curved waveguide 54 has a spiral shape of one turn. The curved waveguide 54 is arranged on the inner side of the curved waveguide 53. The curved waveguide 54 is arranged closer to the second end 58 than the curved waveguide 53. The curved waveguide 54 includes a single maximum curvature portion 54m. The maximum curvature portion 54m is a portion having the largest curvature in the curved waveguide 54. The curved waveguide 54 includes a curved waveguide portion 54a and a curved waveguide portion 54b.

[0058] The curved waveguide portion 54a is connected to the curved waveguide portion 53b. The curved waveguide portion 54a extends toward the outside of the substrate 10 (for example, in the +x direction (see FIG. 1 ) when the principal surface 10a of the substrate 10 is viewed from above. Figure 1 The curved waveguide portion 54a includes a maximum curvature portion 54m. The curved waveguide portion 54b is connected to the curved waveguide portion 54a. The curved waveguide portion 54b is arranged closer to the second end 58 than the curved waveguide portion 54a. The curved waveguide portion 54b extends toward the inner side of the substrate 10 (e.g., in the −x direction (see FIG. 1 )) when the main surface 10a of the substrate 10 is viewed from above. Figure 1 ))Expansion.

[0059] The curved waveguide 55 includes a second end 58 and is connected to the curved waveguide 54. The curved waveguide 55 has a spiral shape of one turn when viewed from above the main surface 10a of the substrate 10. The curved waveguide 55 is arranged on the inner side of the curved waveguide 54. The curved waveguide 55 is arranged closer to the second end 58 than the curved waveguide 54. The curved waveguide 55 includes a single maximum curvature portion 55m. The maximum curvature portion 55m is a portion having the largest curvature in the curved waveguide 55. The curved waveguide 55 includes a curved waveguide portion 55a and a curved waveguide portion 55b.

[0060] The curved waveguide portion 55a is connected to the curved waveguide portion 54b. The curved waveguide portion 55a extends toward the outside of the substrate 10 (for example, in the +x direction (see FIG. 1 ) when the principal surface 10a of the substrate 10 is viewed from above. Figure 1 The curved waveguide portion 55a includes a maximum curvature portion 55m. The curved waveguide portion 55b is connected to the curved waveguide portion 55a. The curved waveguide portion 55b is arranged closer to the second end 58 than the curved waveguide portion 55a. The curved waveguide portion 55b extends toward the inner side of the substrate 10 (e.g., in the −x direction (refer to FIG. 1 )) when the main surface 10a of the substrate 10 is viewed from above. Figure 1 The curved waveguide portion 55b includes the second end 58 of the first terminal waveguide 50.

[0061] In a plan view of the main surface 10a of the substrate 10 (eg Figure 1 as well as Figure 6When viewed from the z direction as shown in the top view, the normal vector of the curved waveguide 51 in the maximum curvature portion 51m, the normal vector of the curved waveguide 52 in the maximum curvature portion 52m, the normal vector of the curved waveguide 53 in the maximum curvature portion 53m, the normal vector of the curved waveguide 54 in the maximum curvature portion 54m, and the normal vector of the curved waveguide 55 in the maximum curvature portion 55m are oriented in the same direction (e.g., +x direction) as each other. When viewed from the top view of the main surface 10a of the substrate 10, the normal vector of the curved waveguide 51 in the maximum curvature portion 51m, the normal vector of the curved waveguide 52 in the maximum curvature portion 52m, the normal vector of the curved waveguide 53 in the maximum curvature portion 53m, the normal vector of the curved waveguide 54 in the maximum curvature portion 54m, and the normal vector of the curved waveguide 55 in the maximum curvature portion 55m are oriented to the outside of the substrate 10 (e.g., +x direction (see FIG. 1 )). Figure 1 )).

[0062] In this specification, a normal vector of a curved waveguide in a portion where the curved waveguide exists is defined as a vector perpendicular to a tangent line of the curved waveguide in the portion when viewed from above the principal surface 10 a of the substrate 10 and extending from the portion in an expansion direction of the curved waveguide.

[0063] like Figure 6 as well as Figure 7 As shown in FIG. 1 , the curvature of the maximum curvature portion 52m is greater than the curvature of the maximum curvature portion 51m. The curvature of the maximum curvature portion 53m is greater than the curvature of the maximum curvature portion 52m. The curvature of the maximum curvature portion 54m is greater than the curvature of the maximum curvature portion 53m. The curvature of the maximum curvature portion 55m is greater than the curvature of the maximum curvature portion 54m. That is, the curvatures of the maximum curvature portions 51m, 52m, 53m, 54m, and 55m increase as they approach the second end 58 of the first terminal waveguide 50.

[0064] like Figure 6 as well as Figure 7 As shown in the figure, in the present embodiment, the curvature of each of the curved waveguide portions 51a, 52a, 53a, 54a, and 55a changes linearly. The curvature of each of the curved waveguide portions 51b, 52b, 53b, 54b, and 55b is constant. However, the curvature of each of the curved waveguide portions 51a, 52a, 53a, 54a, and 55a may change in a non-curved shape. The curvature of each of the curved waveguide portions 51b, 52b, 53b, 54b, and 55b may change.

[0065] (Operation and Function of the Optical Wavelength Filter 1 and the Optical Terminator 30)

[0066] The operation and function of the optical wavelength filter 1 and the optical terminator 30 of this embodiment will be described. The optical terminators 31, 32, and 33 also operate in the same manner as the optical terminator 30 and have the same function as the optical terminator 30.

[0067] Light 40 is incident on the optical wavelength filter 1 from the input port of the ring resonator 20 (the end 11a of the waveguide 11). Light 42 selected by the ring resonator 20 in the light 40 (see Figure 3 ) is incident on the ring resonator 25. Light 46 selected by the ring resonator 25 in the light 42 is incident on the reflector 35. Light 46 is reflected by the reflector 35 and is incident on the waveguide 16. Light 46 is emitted from the end 16a of the waveguide 16 to the outside of the optical wavelength filter 1. Light 41 not selected by the ring resonator 20 in the light 40 is emitted from the optical terminator 30 as radiated light 44 to the outside of the optical wavelength filter 1. Light 42 (refer to Figure 3 ) that is not selected by the ring resonator 25 is radiated from the optical terminator 32 to the outside of the optical wavelength filter 1 as radiated light.

[0068] The radiated light 44 is incident on the spectrum analyzer 48 via the optical fiber 47. The spectrum analyzer 48 obtains the spectrum of the radiated light 44. The controller 49 controls the power supplied to the refractive index adjuster 21 according to the spectrum of the radiated light 44. For example, the power supplied to the refractive index adjuster 21 is adjusted so that the spectral intensity of the wavelength to be selected by the optical wavelength filter 1 in the radiated light 44 from the optical terminator 30 becomes minimum. In this way, the optical coupling factor of the light having the wavelength to be selected by the optical wavelength filter 1 to the drop port of the ring resonator 20 can be maximized. The power supplied to the refractive index adjuster 26 is also controlled by the controller 49 in the same manner as the refractive index adjuster 21. For example, the power supplied to the refractive index adjuster 26 is adjusted according to the radiated light radiated from the optical terminator 32. In this way, the wavelength of the light 46 output from the optical wavelength filter 1 in the light 40 incident on the optical wavelength filter 1 can be adjusted.

[0069] like Figure 6 as well as Figure 7 As shown, the optical terminator 30 includes a plurality of curved waveguides 51, 52, 53, 54, and 55. Therefore, the light 41 (refer to Figure 3 ) is repeatedly radiated from the plurality of curved waveguides 51, 52, 53, 54, and 55. The intensity of the radiated light 44 increases, and the intensity of the light reaching the end (second end 58) of the optical terminator 30 decreases. The optical terminator 30 can further suppress the reflection of light.

[0070] In the optical terminator 30, when the main surface 10a of the substrate 10 is viewed from above (eg Figure 1 as well as Figure 6 (as shown in the top view from the z direction), the normal vector of the curved waveguide 51 in the maximum curvature portion 51m, the normal vector of the curved waveguide 52 in the maximum curvature portion 52m, the normal vector of the curved waveguide 53 in the maximum curvature portion 53m, the normal vector of the curved waveguide 54 in the maximum curvature portion 54m, and the normal vector of the curved waveguide 55 in the maximum curvature portion 55m are oriented in the same direction (for example, the +x direction). Therefore, the radiation direction of the radiated light from the curved waveguide 51, the radiation direction of the radiated light from the curved waveguide 52, the radiation direction of the radiated light from the curved waveguide 53, the radiation direction of the radiated light from the curved waveguide 54, and the radiation direction of the radiated light from the curved waveguide 55 become the same. The directivity of the radiated light 44 radiated from the optical terminator 30 can be improved.

[0071] In a plan view of the principal surface 10a of the substrate 10, the normal vector of the curved waveguide 51 in the maximum curvature portion 51m, the normal vector of the curved waveguide 52 in the maximum curvature portion 52m, the normal vector of the curved waveguide 53 in the maximum curvature portion 53m, the normal vector of the curved waveguide 54 in the maximum curvature portion 54m, and the normal vector of the curved waveguide 55 in the maximum curvature portion 55m are directed toward the outside of the substrate 10 (for example, in the +x direction (see FIG. 2 )). Figure 1 )). Therefore, it becomes easy to extract the radiated light 44 radiated from the optical terminator 30 to the outside of the optical wavelength filter 1. It becomes easy to adjust the selected wavelength of the ring resonator 20 based on the radiated light 44.

[0072] The curvature of the maximum curvature portion 52m is greater than the curvature of the maximum curvature portion 51m. The curvature of the maximum curvature portion 53m is greater than the curvature of the maximum curvature portion 52m. The curvature of the maximum curvature portion 54m is greater than the curvature of the maximum curvature portion 53m. The curvature of the maximum curvature portion 55m is greater than the curvature of the maximum curvature portion 54m. Therefore, the light not emitted from the curved waveguide 51 can be emitted from the curved waveguide 52 more efficiently. The light not emitted from the curved waveguides 51 and 52 can be emitted from the curved waveguide 53 more efficiently. The light not emitted from the curved waveguides 51, 52, and 53 can be emitted from the curved waveguide 54 more efficiently. The light not emitted from the curved waveguides 51, 52, 53, and 54 can be emitted from the curved waveguide 55 more efficiently. Therefore, the intensity of the radiated light 44 is further increased, and the optical terminator 30 can further suppress the reflection of light.

[0073] (Variation Example)

[0074] The reflecting mirror 35 and the waveguide 16 may be omitted, and the light 46 may be emitted from the end 15 a of the waveguide 15 to the outside of the optical wavelength filter 1 .

[0075] When the ring waveguides 12 and 14 are formed of a material having an electro-optical effect (for example, a compound semiconductor material such as InGaAsP), the refractive index adjusters 21 and 26 may be electrodes capable of applying a voltage to the ring waveguides 12 and 14 .

[0076] The shape of the helical waveguide 50a is not limited to a five-turn helical shape, and may be a plurality of turns of helical shape.

[0077] The effects of the optical terminator 30 and the optical wavelength filter 1 of the present embodiment will be described.

[0078] The optical terminator 30 of this embodiment includes a substrate 10 including a main surface 10a and a first terminal waveguide 50 formed on the main surface 10a. The first terminal waveguide 50 includes a first end 57, a first curved waveguide (e.g., curved waveguide 51), a second curved waveguide (e.g., curved waveguide 52), and a second end 58 on the side opposite to the first end 57. The second curved waveguide is connected to the first curved waveguide and is arranged closer to the second end 58 than the first curved waveguide. The first curved waveguide includes a single first maximum curvature portion (e.g., maximum curvature portion 51m). The first maximum curvature portion is a portion having the maximum curvature in the first curved waveguide. The second curved waveguide includes a single second maximum curvature portion (e.g., maximum curvature portion 52m). The second maximum curvature portion is a portion having the maximum curvature in the second curved waveguide. In a plan view of the principal surface 10 a of the substrate 10 , a first normal vector of the first curved waveguide in the first maximum curvature portion and a second normal vector of the second curved waveguide in the second maximum curvature portion are oriented in the same direction.

[0079] Therefore, the light incident on the optical terminator 30 is radiated from the first curved waveguide (e.g., curved waveguide 51) and the second curved waveguide (e.g., curved waveguide 52). The intensity of the radiated light 44 from the first terminal waveguide 50 increases, and the intensity of the light reaching the terminal (second end 58) of the optical terminator 30 decreases. The optical terminator 30 can further suppress the reflection of light. In addition, the first normal vector and the second normal vector are oriented in the same direction, so the directivity of the radiated light 44 radiated from the optical terminator 30 can be improved.

[0080] In the optical terminator 30 of the present embodiment, when the principal surface 10 a of the substrate 10 is viewed from above, the first normal vector and the second normal vector are directed to the outside of the substrate 10 .

[0081] Therefore, it becomes easy to extract the radiated light 44 radiated from the optical terminator 30 to the outside of the substrate 10 .

[0082] In the optical terminator 30 of the present embodiment, the first curved waveguide (e.g., curved waveguide 51) includes a first curved waveguide portion (e.g., curved waveguide portion 51a) that expands toward the outside of the substrate 10 when viewed from above the main surface 10a of the substrate 10, and a second curved waveguide portion (e.g., curved waveguide portion 51b) that expands toward the inside of the substrate 10 when viewed from above the main surface 10a of the substrate 10. The second curved waveguide (e.g., curved waveguide 52) includes a third curved waveguide portion (e.g., curved waveguide portion 52a) that expands toward the outside of the substrate 10 when viewed from above the main surface 10a of the substrate 10, and a fourth curved waveguide portion (e.g., curved waveguide portion 52b) that expands toward the inside of the substrate 10 when viewed from above the main surface 10a of the substrate 10. The first curved waveguide portion includes a first maximum curvature portion (e.g., maximum curvature portion 51m). The third curved waveguide portion includes a second maximum curvature portion (e.g., maximum curvature portion 52m).

[0083] Therefore, it becomes easy to extract the radiated light 44 radiated from the optical terminator 30 to the outside of the substrate 10 .

[0084] In the optical terminator 30 of the present embodiment, the second curvature of the second maximum curvature portion (eg, the maximum curvature portion 52m) is larger than the first curvature of the first maximum curvature portion (eg, the maximum curvature portion 51m).

[0085] Therefore, light that is not emitted from the first curved waveguide (for example, the curved waveguide 51) can be emitted more efficiently from the second curved waveguide (for example, the curved waveguide 52). The optical terminator 30 can further suppress reflection of light.

[0086] In the optical terminator 30 of the present embodiment, the first terminal waveguide 50 is a helical waveguide 50 a in a plan view of the principal surface 10 a of the substrate 10 .

[0087] Therefore, the optical terminator 30 can further suppress the reflection of light, and the directivity of the radiated light 44 radiated from the optical terminator 30 can be improved.

[0088] The optical wavelength filter 1 of the present embodiment includes the optical terminator 30 of the present embodiment, the ring resonator 20, and the refractive index adjuster 21. The ring resonator 20 is connected to the first end 57. The refractive index adjuster 21 adjusts the refractive index of the ring resonator 20.

[0089] The radiated light 44 from the optical terminator 30 has higher intensity and higher directivity. Therefore, the wavelength of the light selected by the optical wavelength filter 1 can be adjusted more accurately based on the radiated light 44 from the optical terminator 30.

[0090] Implementation method 2.

[0091] Reference Figure 1 , Figure 8as well as Fig. 9 , the optical wavelength filter 1 of the second embodiment is described. The optical wavelength filter 1 of this embodiment has the same structure as the optical wavelength filter 1 of the first embodiment and has the same effect, but is different from the optical wavelength filter 1 of the first embodiment in the optical terminators 30, 31, 32, and 33. In the optical wavelength filter 1 of this embodiment, the optical terminators 31, 32, and 33 are also configured in the same manner as the optical terminator 30 and function in the same manner. Therefore, referring to Figure 8 as well as Fig. 9 , the optical terminator 30 of this embodiment is described in detail.

[0092] In this embodiment, when the main surface 10a of the substrate 10 is viewed from above (eg Figure 1 as well as Figure 8 The first terminal waveguide 50 is a first meander waveguide 50b (as shown in the figure when viewed from the z direction). The bending direction of the first meander waveguide 50b is the x direction, and the bending direction of the first meander waveguide 50b is the +y direction. The first meander waveguide 50b is bent seven times. The first terminal waveguide 50 includes a first end 57, curved waveguides 51, 52, 53, 54, and a second end 58 on the side opposite to the first end 57.

[0093] The first end 57 of the first terminal waveguide 50 is connected to the end 11b of the waveguide 11, which is the through port of the ring resonator 20. The first end 57 is the optical input end of the optical terminator 30. The second end 58 is the terminal of the optical terminator 30.

[0094] The curved waveguide 51 includes a first end 57 of the first terminal waveguide 50, and is connected to the end 11b of the waveguide 11. The curved waveguide 51 is bent twice. The curved waveguide 51 includes a single maximum curvature portion 51m. The maximum curvature portion 51m is a portion having the largest curvature in the curved waveguide 51. The curved waveguide 51 includes a curved waveguide portion 51a, a curved waveguide portion 51b, a straight waveguide portion 51c, and a straight waveguide portion 51d.

[0095] The curved waveguide portion 51a is connected to the waveguide 11 and includes the first end 57 of the first terminal waveguide 50. The curved waveguide portion 51a is bent once. The curved waveguide portion 51a is directed toward the outside of the substrate 10 (e.g., in the +x direction (see FIG. 1 ) when the main surface 10a of the substrate 10 is viewed from above. Figure 1 )) is expanded. The curved waveguide portion 51a includes a maximum curvature portion 51m. The straight waveguide portion 51c is connected to the curved waveguide portion 51a. The straight waveguide portion 51c is arranged closer to the second end 58 than the curved waveguide portion 51a. The straight waveguide portion 51c extends in a direction (x direction) perpendicular to the bending direction of the first meandering waveguide 50b.

[0096] The curved waveguide portion 51b is connected to the straight waveguide portion 51c. The curved waveguide portion 51b is arranged closer to the second end 58 than the straight waveguide portion 51c. The curved waveguide portion 51b is bent once. The curved waveguide portion 51b is directed toward the inner side of the substrate 10 (e.g., in the −x direction (see FIG. 1 )) when the main surface 10a of the substrate 10 is viewed from above. Figure 1 The straight waveguide portion 51d is connected to the curved waveguide portion 51b. The straight waveguide portion 51d is arranged closer to the second end 58 than the curved waveguide portion 51b. The straight waveguide portion 51d extends in a direction (x direction) perpendicular to the bending direction of the first meandering waveguide 50b.

[0097] The curved waveguide 52 is connected to the curved waveguide 51. The curved waveguide 52 is arranged on the side opposite to the waveguide 11 (+y side) with respect to the curved waveguide 51. The curved waveguide 52 is arranged closer to the second end 58 than the curved waveguide 51. The curved waveguide 52 is bent twice. The curved waveguide 52 includes a single maximum curvature portion 52m. The maximum curvature portion 52m is a portion having the largest curvature in the curved waveguide 52. The curved waveguide 52 includes a curved waveguide portion 52a, a curved waveguide portion 52b, a straight waveguide portion 52c, and a straight waveguide portion 52d.

[0098] The curved waveguide portion 52a is connected to the straight waveguide portion 51d. The curved waveguide portion 52a is bent once. The curved waveguide portion 52a is directed toward the outside of the substrate 10 (for example, in the +x direction (see Figure 1 )) is expanded. The curved waveguide portion 52a includes a maximum curvature portion 52m. The straight waveguide portion 52c is connected to the curved waveguide portion 52a. The straight waveguide portion 52c is arranged closer to the second end 58 than the curved waveguide portion 52a. The straight waveguide portion 52c extends in a direction (x direction) perpendicular to the bending direction of the first meandering waveguide 50b.

[0099] The curved waveguide portion 52b is connected to the straight waveguide portion 52c. The curved waveguide portion 52b is arranged closer to the second end 58 than the straight waveguide portion 52c. The curved waveguide portion 52b is bent once. The curved waveguide portion 52b is directed toward the inner side of the substrate 10 (e.g., in the −x direction (see FIG. 1 )) when the main surface 10a of the substrate 10 is viewed from above. Figure 1 The straight waveguide portion 52d is connected to the curved waveguide portion 52b. The straight waveguide portion 52d is arranged closer to the second end 58 than the curved waveguide portion 52b. The straight waveguide portion 52d extends in a direction (x direction) perpendicular to the bending direction of the first meandering waveguide 50b.

[0100] The curved waveguide 53 is connected to the curved waveguide 52. The curved waveguide 53 is arranged on the side opposite to the waveguide 11 (+y side) with respect to the curved waveguide 52. The curved waveguide 53 is arranged closer to the second end 58 than the curved waveguide 52. The curved waveguide 53 is bent twice. The curved waveguide 53 includes a single maximum curvature portion 53m. The maximum curvature portion 53m is a portion having the largest curvature in the curved waveguide 53. The curved waveguide 53 includes a curved waveguide portion 53a, a curved waveguide portion 53b, a straight waveguide portion 53c, and a straight waveguide portion 53d.

[0101] The curved waveguide portion 53a is connected to the straight waveguide portion 52d. The curved waveguide portion 53a is bent once. The curved waveguide portion 53a is directed toward the outside of the substrate 10 (for example, in the +x direction (see Figure 1 )) is expanded. The curved waveguide portion 53a includes a maximum curvature portion 53m. The straight waveguide portion 53c is connected to the curved waveguide portion 53a. The straight waveguide portion 53c is arranged closer to the second end 58 than the curved waveguide portion 53a. The straight waveguide portion 53c extends in a direction (x direction) perpendicular to the bending direction of the first meandering waveguide 50b.

[0102] The curved waveguide portion 53b is connected to the straight waveguide portion 52d. The curved waveguide portion 53b is arranged closer to the second end 58 than the straight waveguide portion 53c. The curved waveguide portion 53b is bent once. The curved waveguide portion 53b is directed toward the inner side of the substrate 10 (e.g., in the −x direction (see FIG. 1 )) when the main surface 10a of the substrate 10 is viewed from above. Figure 1 The straight waveguide portion 53d is connected to the curved waveguide portion 53b. The straight waveguide portion 53d is arranged closer to the second end 58 than the curved waveguide portion 53b. The straight waveguide portion 53d extends in a direction (x direction) perpendicular to the bending direction of the first meandering waveguide 50b.

[0103] The curved waveguide 54 is connected to the curved waveguide 53. The curved waveguide 54 is arranged on the side opposite to the waveguide 11 (+y side) with respect to the curved waveguide 53. The curved waveguide 54 is arranged closer to the second end 58 than the curved waveguide 53. The curved waveguide 54 is bent once. The curved waveguide 54 includes a single maximum curvature portion 54m. The maximum curvature portion 54m is a portion having the largest curvature in the curved waveguide 54. The curved waveguide 54 includes a curved waveguide portion 54a, a curved waveguide portion 54b, and a straight waveguide portion 54c.

[0104] The curved waveguide portion 54a is connected to the straight waveguide portion 53d. The curved waveguide portion 54a is bent once. The curved waveguide portion 54a is directed toward the outside of the substrate 10 (for example, in the +x direction (see FIG. 1 ) when the principal surface 10a of the substrate 10 is viewed from above. Figure 1)) is expanded. The curved waveguide portion 54a includes a maximum curvature portion 54m. The straight waveguide portion 54c is connected to the curved waveguide portion 54a. The straight waveguide portion 54c is arranged closer to the second end 58 than the curved waveguide portion 54a. The straight waveguide portion 54c extends in a direction (x direction) perpendicular to the bending direction of the first meandering waveguide 50b. The straight waveguide portion 54c includes the second end 58 of the first terminal waveguide 50.

[0105] In a plan view of the main surface 10a of the substrate 10 (eg Figure 1 as well as Figure 8 When viewed from the z direction as shown in the top view, the normal vector of the curved waveguide 51 in the maximum curvature portion 51m, the normal vector of the curved waveguide 52 in the maximum curvature portion 52m, the normal vector of the curved waveguide 53 in the maximum curvature portion 53m, and the normal vector of the curved waveguide 54 in the maximum curvature portion 54m are oriented in the same direction (e.g., +x direction). When viewed from the top view of the main surface 10a of the substrate 10, the normal vector of the curved waveguide 51 in the maximum curvature portion 51m, the normal vector of the curved waveguide 52 in the maximum curvature portion 52m, the normal vector of the curved waveguide 53 in the maximum curvature portion 53m, and the normal vector of the curved waveguide 54 in the maximum curvature portion 54m are oriented to the outside of the substrate 10 (e.g., +x direction (see FIG. 1 )). Figure 1 )).

[0106] like Figure 8 as well as Fig. 9 As shown, the curvature of the maximum curvature portion 51m, the curvature of the maximum curvature portion 52m, the curvature of the maximum curvature portion 53m, and the curvature of the maximum curvature portion 54m are equal to each other.

[0107] like Figure 8 as well as Fig. 9 As shown in the figure, in the present embodiment, the curvature of each of the curved waveguide portions 51a, 52a, 53a, and 54a changes linearly. The curvature of each of the curved waveguide portions 51b, 52b, and 53b changes linearly. However, the curvature of each of the curved waveguide portions 51a, 52a, 53a, and 54a may change in a non-curved shape. The curvature of each of the curved waveguide portions 51b, 52b, and 53b may change in a non-curved shape or may be constant.

[0108] The optical terminator 30 of this embodiment has the same function as the optical terminator 30 of Embodiment 1. In addition, the optical terminators 31, 32, and 33 also have the same function as the optical terminator 30.

[0109] Specifically, if Figure 8 as well as Fig. 9As shown, the optical terminator 30 includes a plurality of curved waveguides 51, 52, 53, and 54. Therefore, the light 41 (refer to Figure 3 ) is repeatedly radiated from the plurality of curved waveguides 51, 52, 53, and 54. The intensity of the radiated light 44 increases, and the intensity of the light reaching the end (second end 58) of the optical terminator 30 decreases. The optical terminator 30 can further suppress the reflection of light.

[0110] In the optical terminator 30, when the main surface 10a of the substrate 10 is viewed from above (eg Figure 1 as well as Figure 8 (as shown in the top view from the z direction), the normal vector of the curved waveguide 51 in the maximum curvature portion 51m, the normal vector of the curved waveguide 52 in the maximum curvature portion 52m, the normal vector of the curved waveguide 53 in the maximum curvature portion 53m, and the normal vector of the curved waveguide 54 in the maximum curvature portion 54m are oriented in the same direction (for example, the +x direction). Therefore, the radiation direction of the radiated light from the curved waveguide 51, the radiation direction of the radiated light from the curved waveguide 52, the radiation direction of the radiated light from the curved waveguide 53, and the radiation direction of the radiated light from the curved waveguide 54 become the same. The directivity of the radiated light 44 radiated from the optical terminator 30 can be improved.

[0111] In a plan view of the principal surface 10a of the substrate 10, the normal vector of the curved waveguide 51 in the maximum curvature portion 51m, the normal vector of the curved waveguide 52 in the maximum curvature portion 52m, the normal vector of the curved waveguide 53 in the maximum curvature portion 53m, and the normal vector of the curved waveguide 54 in the maximum curvature portion 54m are oriented toward the outside of the substrate 10 (for example, in the +x direction (see Figure 1 )). Therefore, it becomes easy to extract the radiated light 44 radiated from the optical terminator 30 to the outside of the optical wavelength filter 1. It becomes easy to adjust the selected wavelength of the ring resonator 20 based on the radiated light 44.

[0112] (Variation Example)

[0113] Reference Fig.10 as well as Fig.11 In the modified example of the present embodiment, the curvature of the maximum curvature portion 52m is greater than the curvature of the maximum curvature portion 51m. The curvature of the maximum curvature portion 53m is greater than the curvature of the maximum curvature portion 52m. The curvature of the maximum curvature portion 54m is greater than the curvature of the maximum curvature portion 53m. That is, the curvatures of the maximum curvature portions 51m, 52m, 53m, and 54m increase as they approach the second end 58 of the first terminal waveguide 50.

[0114] Therefore, light not emitted from the curved waveguide 51 can be emitted more efficiently from the curved waveguide 52. Light not emitted from the curved waveguides 51 and 52 can be emitted more efficiently from the curved waveguide 53. Light not emitted from the curved waveguides 51, 52, and 53 can be emitted more efficiently from the curved waveguide 54. In the modified example of the present embodiment, reflection of light in the optical terminator 30 can be further suppressed.

[0115] The linear waveguide portions 51 c , 51 d , 52 c , 52 d , 53 c , 53 d , and 54 c may be omitted from the first terminal waveguide 50 .

[0116] The optical terminator 30 of this embodiment achieves the following effects similar to those of the optical terminator 30 of Embodiment 1. The optical wavelength filter 1 of this embodiment achieves the same effects as those of the optical wavelength filter 1 of Embodiment 1.

[0117] In the optical terminator 30 of the present embodiment, the first terminal waveguide 50 is a first meandering waveguide 50 b in a plan view of the principal surface 10 a of the substrate 10 .

[0118] Therefore, the optical terminator 30 can further suppress the reflection of light, and the directivity of the radiated light 44 radiated from the optical terminator 30 can be improved.

[0119] Implementation method 3.

[0120] Reference Figure 1 as well as Fig.12 , the optical wavelength filter 1 of the third embodiment is described. The optical wavelength filter 1 of the present embodiment has the same structure as the optical wavelength filter 1 of the first embodiment and has the same effect, but is different from the optical wavelength filter 1 of the first embodiment in the optical terminators 30, 31, 32, and 33. In the optical wavelength filter 1 of the present embodiment, the optical terminators 31, 32, and 33 are also configured in the same manner as the optical terminator 30 and function in the same manner. Therefore, referring to Fig.12 , the optical terminator 30 of this embodiment is described in detail.

[0121] The optical terminator 30 of the present embodiment further includes reflection elements 61 and 62. The reflection elements 61 and 62 are, for example, reflection grooves formed in the cladding (upper cladding 18 and lower cladding 17). The reflection elements 61 and 62 are arranged away from the first terminal waveguide 50. The reflection elements 61 and 62 reflect the leakage light 45a and 45b that leaks from the first terminal waveguide 50 and travels in a direction different from the radiated light 44, and make the leakage light 45a and 45b travel in the same direction as the radiated light 44 (for example, the outside of the substrate 10 (for example, the +x direction (refer to Figure 1 ))). The leaked light 45a and 45b become part of the radiated light 44.

[0122] For example, the reflective elements 61 and 62 are arranged in a direction (y direction) perpendicular to the direction (+x direction) of the normal vector of each of the maximum curvature portions 51m, 52m, 53m, 54m, and 55m with respect to the first terminal waveguide 50. For example, the reflective element 61 is arranged in the -y direction with respect to the first terminal waveguide 50. The reflective element 62 is arranged in the +y direction with respect to the first terminal waveguide 50. The reflective elements 61 and 62 may be respectively arranged opposite to the curved waveguide portion 51b.

[0123] (Variation Example)

[0124] The optical terminator 30 only needs to include at least one reflecting element.

[0125] For example, the reflective elements 61 and 62 may be arranged in the first terminal waveguide 50 in the direction (−x direction) opposite to the direction (+x direction) of the normal vector of each of the maximum curvature portions 51 m , 52 m , 53 m , 54 m , and 55 m .

[0126] The first terminal waveguide 50 of the second embodiment and its modified example (see Figure 8 as well as Fig.10 ), at least one reflective element (for example, reflective elements 61, 62) is provided in the same manner as in the present embodiment.

[0127] The optical terminator 30 and the optical wavelength filter 1 of the present embodiment provide the following effects in addition to the effects of the optical terminator 30 and the optical wavelength filter 1 of the first embodiment.

[0128] The optical terminator 30 of this embodiment further includes reflection elements 61 and 62 disposed away from the first terminal waveguide 50. The reflection elements 61 and 62 reflect the leakage lights 45a and 45b from the first terminal waveguide 50 and direct the leakage lights 45a and 45b to the outside of the substrate 10.

[0129] Therefore, the intensity of the radiated light 44 radiated from the optical terminator 30 is increased. Based on the radiated light 44 from the optical terminator 30, the wavelength of the light selected by the optical wavelength filter 1 can be adjusted more accurately.

[0130] Implementation method 4.

[0131] Reference Figure 1 as well as Fig.13 The optical wavelength filter 1 of the fourth embodiment is described. The optical wavelength filter 1 of the present embodiment has the same configuration as the optical wavelength filter 1 of the second embodiment (see Figure 1 , Figure 8 as well as Fig. 9) has the same structure and the same effect, but the optical terminators 30, 31, 32, and 33 are different from the optical wavelength filter 1 of the second embodiment. In the optical wavelength filter 1 of this embodiment, the optical terminators 31, 32, and 33 are also configured in the same manner as the optical terminator 30 and function in the same manner. Therefore, referring to Fig.13 , the optical terminator 30 of this embodiment is described in detail.

[0132] The optical terminator 30 of the present embodiment further includes a second terminal waveguide 66. The second terminal waveguide 66 is connected to the second end 58 of the first terminal waveguide 50. The second terminal waveguide 66 is connected to the second end 58 of the first terminal waveguide 50, which means that the second terminal waveguide 66 is directly connected to the second end 58 of the first terminal waveguide 50 or the second terminal waveguide 66 is connected to the second end 58 of the first terminal waveguide 50 via the straight waveguide portion 65. Figure 1 as well as Fig.13 The second terminal waveguide 66 is a spiral waveguide 66a (as shown in the plan view from the z direction). The terminal 67 of the second terminal waveguide 66 is the terminal of the optical terminator 30.

[0133] The second terminal waveguide 66 is opposite to the waveguide 11 in the bending direction (+y direction) of the first zigzag waveguide 50b. The second terminal waveguide 66 is opposite to the first zigzag waveguide 50b in the bending direction (x direction) of the first zigzag waveguide 50b. More specifically, the second terminal waveguide 66 is opposite to at least one of the curved waveguide portions 51b, 52b, and 53b in the bending direction (x direction) of the first zigzag waveguide 50b. The second terminal waveguide 66 is arranged at the same position as the second end 58 of the first terminal waveguide 50 in the bending direction (+y direction) of the first zigzag waveguide 50b or is arranged on the side (-y side) opposite to the bending direction (+y direction) of the first zigzag waveguide 50b with respect to the second end 58 of the first terminal waveguide 50. The second terminal waveguide 66 is not arranged on the one side (+y side) of the bending advancing direction of the first meandering waveguide 50 b with respect to the second end 58 of the first terminal waveguide 50 .

[0134] (Variation Example)

[0135] Reference Fig.14In a modified example of the present embodiment, when viewed from above the main surface 10a of the substrate 10, the second terminal waveguide 66 is a second meander waveguide 66b. The bending direction of the second meander waveguide 66b is, for example, along the bending direction (+y direction) of the first meander waveguide 50b. Specifically, the bending direction of the second meander waveguide 66b is the y direction. The bending direction of the second meander waveguide 66b is, for example, along the bending direction (x direction) of the first meander waveguide 50b. Specifically, the bending direction of the second meander waveguide 66b is the -x direction. The bending direction of the second meander waveguide 66b is, for example, a direction opposite to the direction of the normal vector of the first meander waveguide 50b in each of the maximum curvature portions 51m, 52m, 53m, and 54m.

[0136] The optical terminator 30 of this embodiment has the following effects in addition to the effects of the optical terminator 30 of the first embodiment.

[0137] The optical terminator 30 of the present embodiment further includes a second terminal waveguide 66 connected to the second end 58. The second terminal waveguide 66 faces the first meandering waveguide 50b in the bending direction of the first meandering waveguide 50b.

[0138] Therefore, the light incident on the optical terminator 30 is radiated from the second terminal waveguide 66 in addition to the first terminal waveguide 50. The intensity of the light reaching the terminal (terminal 67) of the optical terminator 30 is further reduced. The optical terminator 30 can further suppress the reflection of light. In addition, the second terminal waveguide 66 is opposed to the first zigzag waveguide 50b in the bending direction of the first zigzag waveguide 50b, so the optical terminator 30 can be miniaturized.

[0139] In the optical terminator 30 of the present embodiment, the second terminal waveguide 66 is a helical waveguide 66 a in a plan view of the principal surface 10 a of the substrate 10 .

[0140] Therefore, the intensity of light reaching the terminal (terminal 67) of the optical terminator 30 is further reduced. The optical terminator 30 can further suppress reflection of light. The optical terminator 30 can be miniaturized.

[0141] In the optical terminator 30 of the present embodiment, the second terminal waveguide 66 is a second meandering waveguide 66 b in a plan view of the principal surface 10 a of the substrate 10 .

[0142] Therefore, the intensity of light reaching the terminal (terminal 67) of the optical terminator 30 is further reduced. The optical terminator 30 can further suppress the reflection of light. The optical terminator 30 can be miniaturized.

[0143] Implementation method 5.

[0144] Reference Fig.15 as well as Fig.16Next, an external resonator type laser light source 2 according to Embodiment 5 is described. The external resonator type laser light source 2 according to this embodiment includes the optical wavelength filter 1 according to Embodiment 1, an optical amplifier 70 , and a reflecting mirror 80 .

[0145] like Fig.16 As shown, the optical amplifier 70 is, for example, a semiconductor optical amplifier (SOA). Specifically, the optical amplifier 70 includes a semiconductor substrate 71 , a lower cladding layer 72 , an active layer 73 , an upper cladding layer 74 , a contact layer 75 , a current blocking layer 76 , an electrode 77 , and an insulating protection film 79 .

[0146] The semiconductor substrate 71 is formed of a semiconductor material such as InP, for example. The lower cladding layer 72 is formed on the semiconductor substrate 71. The lower cladding layer 72 is, for example, an n-type semiconductor layer. The lower cladding layer 72 is, for example, an n-type InP layer.

[0147] The active layer 73 is formed on the lower cladding layer 72. The active layer 73 has a smaller band gap energy than the lower cladding layer 72 and the upper cladding layer 74, and has a higher refractive index than the lower cladding layer 72 and the upper cladding layer 74. The active layer 73 is, for example, a multiple quantum well (MQW) layer formed of AlGaInAs.

[0148] The upper cladding layer 74 is formed on the active layer 73. The upper cladding layer 74 has a conductivity type opposite to that of the lower cladding layer 72. The upper cladding layer 74 is, for example, a p-type semiconductor layer. The upper cladding layer 74 is, for example, a p-type InP layer. The contact layer 75 is formed on the upper cladding layer 74. The contact layer 75 is a semiconductor layer having the same conductivity type as the upper cladding layer 74 and having a lower resistance than the upper cladding layer 74. The contact layer 75 is, for example, a p-type InGaAs layer.

[0149] The electrode 77 is formed on the contact layer 75. The electrode 77 is a single metal layer or a multi-layer metal layer formed of a metal material such as Ti, Au, Pt, Nb or Ni. Current is injected into the active layer 73 from the electrode 77. Light as natural emission light (ASE) is emitted from the active layer 73. The light reflected by the reflector 35 and the reflector 80 is amplified in the active layer 73.

[0150] Current blocking layers 76 are disposed on both sides of the active layer 73. The current blocking layer 76 prevents the current injected from the electrode 77 from flowing into the current blocking layer 76 and concentrates the current into the active layer 73. The current blocking layer 76 diffuses the heat generated in the active layer 73. Therefore, it is possible to suppress the reduction in the gain of the active layer 73 caused by the temperature rise of the active layer 73. The current blocking layer 76 is, for example, a semi-insulating semiconductor layer such as an InP layer to which Fe is added, or a semiconductor stack in which p-type semiconductor layers and n-type semiconductor layers are alternately stacked.

[0151] The insulating protective film 79 covers the outer surfaces of the semiconductor layers (e.g., the lower cladding layer 72, the active layer 73, the upper cladding layer 74, the contact layer 75, and the current blocking layer 76) constituting the optical amplifier 70. The insulating protective film 79 prevents the semiconductor layers constituting the optical amplifier 70 from being oxidized or deteriorated due to moisture or oxygen contained in the atmosphere around the optical amplifier 70. The insulating protective film 79 is formed of, for example, an inorganic oxide film such as SiO2, an inorganic nitride film such as SiN, or an organic insulating film such as benzocyclobutene (BCB).

[0152] like Fig.16 As shown, the optical amplifier 70 includes an end face 70a and an end face 70b on the side opposite to the end face 70a. The end face 70a is opposite to the end 11a of the waveguide 11 which is the incident end of the optical wavelength filter 1. The optical amplifier 70 is optically coupled to the end 11a of the waveguide 11. The end face 70b is opposite to the reflector 80. The reflector 35 and the reflector 80 form an external resonator in the external resonator type laser light source 2. The optical amplifier 70 and the ring resonators 20 and 25 are arranged between the reflector 35 and the reflector 80.

[0153] The operation of the external resonator type laser light source 2 will be described. When a current is injected from the electrode 77 into the active layer 73, spontaneous emission light (ASE) is emitted from the active layer 73. The light emitted from the active layer 73 is coupled to the waveguide 11, and is reflected by the reflector 35 and the reflector 80, and resonates between the reflector 35 and the reflector 80. The light having the wavelength selected by the optical wavelength filter 1 among the light emitted from the active layer 73 is amplified by the optical amplifier 70. The external resonator type laser light source 2 outputs the light 46 as laser light from the end 16a of the waveguide 16.

[0154] (effect)

[0155] Since the external resonator type laser light source 2 includes the optical terminators 30, 31, 32, and 33, the reflected return light incident on the optical amplifier 70 is reduced. The optical terminators 30, 31, 32, and 33 can stabilize the laser oscillation of the external resonator type laser light source 2.

[0156] In order to operate the external resonator laser light source 2, it is necessary to correctly align the optical amplifier 70 with the optical wavelength filter 1 and appropriately set the selected wavelengths of the ring resonators 20 and 25. However, before the optical amplifier 70 is correctly aligned with the optical wavelength filter 1 or the selected wavelengths of the ring resonators 20 and 25 are appropriately set, the external resonator laser light source 2 does not oscillate laser light, and the light 46 output from the output end (end 16a) of the optical wavelength filter 1 is extremely weak. Therefore, it is impossible to align the optical amplifier 70 with respect to the optical wavelength filter 1 and set the selected wavelengths of the ring resonators 20 and 25 using the light 46.

[0157] In contrast, in the present embodiment, the radiated light 44 having higher intensity and higher directivity is radiated from the optical terminator 30. Before the optical amplifier 70 is correctly aligned with the optical wavelength filter 1 or before the selected wavelengths of the ring resonators 20 and 25 are appropriately set, the intensity of the radiated light 44 radiated from the optical terminator 30 is greater than the intensity of the light 46. The intensity of the radiated light radiated from the optical terminator 32 is also greater than the intensity of the light 46, similarly to the radiated light 44. Therefore, the optical amplifier 70 can be correctly aligned with the optical wavelength filter 1 and the selected wavelength of the ring resonator 20 can be appropriately set based on the radiated light 44 radiated from the optical terminator 30. In addition, the selected wavelength of the ring resonator 25 can be appropriately set based on the radiated light radiated from the optical terminator 32.

[0158] Specifically, when current is injected from the electrode 77 into the active layer 73, spontaneous emission light (ASE light) is output from the active layer 73. The ASE light has a wavelength band of about 50 nm, for example. Light having a wavelength other than the wavelength of the light coupled to the ring resonator 20, 25 among the ASE light is emitted from the optical terminator 30 as the emission light 44 or emitted from the optical terminator 32 as the emission light. When the optical amplifier 70 is correctly aligned to the optical wavelength filter 1, the intensity of the emission light 44 emitted from the optical terminator 30 becomes maximum. Therefore, by moving the optical amplifier 70 relative to the optical wavelength filter 1 so that the intensity of the emission light 44 becomes maximum, the optical amplifier 70 is correctly aligned to the optical wavelength filter 1.

[0159] Thereafter, as described in Embodiment 1, the current supplied to the refractive index adjuster 21 is adjusted so that the spectral intensity of the wavelength to be selected by the optical wavelength filter 1 in the radiated light 44 from the optical terminator 30 becomes minimum. The current supplied to the refractive index adjuster 26 is adjusted so that the spectral intensity of the wavelength to be selected by the optical wavelength filter 1 in the radiated light from the optical terminator 32 becomes minimum. In this way, the selected wavelengths of the ring resonators 20 and 25 can be accurately set, and the selected wavelength of the optical wavelength filter 1 can be accurately set.

[0160] (Variation Example)

[0161] The external resonator type laser light source 2 may include any of the optical wavelength filters 1 in Embodiments 2 to 4 instead of the optical wavelength filter 1 in Embodiment 1.

[0162] The effects of the external cavity type laser light source 2 of this embodiment will be described.

[0163] The external cavity laser light source 2 of the present embodiment includes an optical wavelength filter 1 and an optical amplifier 70 optically coupled to the ring resonator 20 .

[0164] Therefore, even without oscillating the external resonator laser source 2 , the optical amplifier 70 can be more accurately aligned with the optical wavelength filter 1 and the selected wavelength of the optical wavelength filter 1 can be set using the radiated light emitted from the optical terminators 30 and 32 .

[0165] The embodiments 1-5 and their modifications disclosed herein are illustrative and non-restrictive in all aspects. As long as there is no contradiction, at least two of the embodiments 1-5 and their modifications disclosed herein may be combined. The scope of the present disclosure is not shown by the above description but by the claims, and is intended to include all changes within the meaning and scope equivalent to the claims.

[0166] (Explanation of symbols)

[0167] 1: optical wavelength filter; 2: external resonator type laser light source; 10: substrate; 10a: main surface; 11, 13, 15, 16: waveguide; 11a, 11b, 13a, 13b, 15a, 15b, 16a, 16b: end; 12, 14: ring waveguide; 17: lower cladding; 18: upper cladding; 20, 25: ring resonator; 21, 26: refractive index adjuster ; 22, 23, 27, 28: electrode pads; 30, 31, 32, 33: optical terminator; 35, 80: reflector; 40, 41, 42, 46: light; 44: radiated light; 45a, 45b: leakage light; 47: optical fiber; 48: spectrum analyzer; 49: controller; 50: first terminal waveguide; 50a: spiral waveguide; 50b: first meander waveguide; 51, 52 , 53, 54, 55: curved waveguide; 51a, 51b, 52a, 52b, 53a, 53b, 54a, 54b, 55a, 55b: curved waveguide part; 51c, 51d, 52c, 52d, 53c, 53d, 54c, 65: straight waveguide part; 51m, 52m, 53m, 54m, 55m: maximum curvature part; 57: first end; 5 8: the second end; 61, 62: reflecting element; 66: the second terminal waveguide; 66a: the spiral waveguide; 66b: the second meander waveguide; 67: the terminal; 70: the optical amplifier; 70a, 70b: the end face; 71: the semiconductor substrate; 72: the lower cladding; 73: the active layer; 74: the upper cladding; 75: the contact layer; 76: the current blocking layer; 77: the electrode; 79: the insulating protective film.

Claims

1. An optical terminal comprising: a substrate including a main surface; and A first terminal waveguide is formed on the main surface, The first terminal waveguide includes a first end, a first curved waveguide, a second curved waveguide, and a second end on the opposite side to the first end. The second curved waveguide is connected to the first curved waveguide and is arranged closer to the second end than the first curved waveguide. The first curved waveguide includes a unique first maximum curvature portion, and the first maximum curvature portion is a portion of the first curved waveguide having a maximum curvature. The second curved waveguide includes a unique second maximum curvature portion, and the second maximum curvature portion is a portion of the second curved waveguide having a maximum curvature. In a plan view of the main surface, a first normal vector of the first curved waveguide in the first maximum curvature portion and a second normal vector of the second curved waveguide in the second maximum curvature portion are oriented in the same direction.

2. The optical terminator according to claim 1, wherein: In the plan view of the main surface, the first normal vector and the second normal vector are directed toward the outside of the substrate.

3. The optical terminator according to claim 1, wherein: The first curved waveguide includes a first curved waveguide portion that expands toward the outside of the substrate when viewed from above the main surface, and a second curved waveguide portion that expands toward the inside of the substrate when viewed from above the main surface. The second curved waveguide includes a third curved waveguide portion that expands toward the outside of the substrate when viewed from above the main surface, and a fourth curved waveguide portion that expands toward the inside of the substrate when viewed from above the main surface. The first curved waveguide portion includes the first maximum curvature portion, The third curved waveguide portion includes the second maximum curvature portion.

4. The optical terminator according to claim 2 or 3, wherein: further comprising a reflective element disposed away from the first terminal waveguide, The reflective element reflects leakage light from the first terminal waveguide and directs the leakage light toward the outside of the substrate.

5. The optical terminator according to any one of claims 1 to 4, wherein: A second curvature of the second maximum curvature portion is greater than a first curvature of the first maximum curvature portion.

6. The optical terminator according to any one of claims 1 to 5, wherein: In the plan view of the main surface, the first terminal waveguide is a helical waveguide.

7. The optical terminator according to any one of claims 1 to 5, wherein: In the plan view of the main surface, the first terminal waveguide is a first meandering waveguide.

8. The optical terminator according to claim 7, wherein: further comprising a second terminal waveguide connected to the second end, The second terminal waveguide is opposed to the first meandering waveguide in a bending direction of the first meandering waveguide.

9. The optical terminator according to claim 8, wherein: In the plan view of the main surface, the second terminal waveguide is a helical waveguide.

10. The optical terminator according to claim 8, wherein: In the plan view of the main surface, the second terminal waveguide is a second meandering waveguide.

11. An optical wavelength filter comprising: The optical terminal according to any one of claims 1 to 10; a ring resonator connected to the first end; and A refractive index adjuster is used to adjust the refractive index of the ring resonator.

12. An external resonator laser light source, comprising: The optical wavelength filter of claim 11; and An optical amplifier is optically coupled to the ring resonator.

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